This invention relates to a hub for taking up a magnetic tape, for use in the slitting of magnetic film into widths of cassette tapes or open tapes.
When a broad film for magnetic tape is slitted into a plurality of tapes with widths for cassettes or open reels, the common practice is to wind the tapes on a plurality of flangeless take-up hubs mounted on a driving shaft. To keep the tapes out of contact, the take-up hubs during the winding operation must be disposed in a certain spaced relation.
The hubs laden with magnetic tape rolls are removed from the slitter and are either conveyed to the next station or stored temporarily. When the hubs are laid horizontally and stacked on one sides, gaps between the adjacent hubs and between their tape rolls can present a stepwise collapse problem of the tape rolls upon subjection to some external forces due to vibration, impact, etc. or because of their own weight.
Means for solving the problems are taught by Japanese Utility Model Application Publication No. 44316/1986, U.S. Pat. Nos. 4,081,151, 4,201,353, 4,280,670, etc. None of them are fully satisfactory because their advantages are more or less offset by their disadvantages. First, Utility Model Application Publication No. 44316/1986 discloses a hub whose circular ring, thicker than the width of a tape to be taken up is formed with large recesses in given portions on both sides and bumps or protrusions of a given height in portions diametrally opposite to the recesses so as to fit in the recesses of adjacent circular rings. The hub, therefore, is complex in shape and poorly symmetric. When adjacent hubs, in a stack with their protrusions in contact, are mounted on a driving shaft, the spacing is instable because of uneven spacer action. When the stack is demounted from the driving shaft and kept closer by fitting the protrusions in the recesses of the neighboring hubs, every other hub must be turned either way through an angle of 180 deg., in a cumbersome procedure. U.S. Pat. No. 4,081,151 introduces a hub whose circular ring has three recesses formed on one side with corresponding protrusions formed on the reverse side. Superposing a plurality of hubs in a stack brings their circular rings into close contact as the protrusions on one side are fitly engaged with the recesses on the other side of the next circular ring and so forth. However, since each hub is not identically shaped on both sides, the close-contact superposition is not accomplished unless all the hubs are oriented in the same direction.
U.S. Pat. Nos. 4,201,353 and 4,280,670 reveal hubs having the same configuration on both sides with good symmetry. Typical of them is a tape take-up hub which, as shown in FIG. 6, comprises a circular ring 7 having an outer wall surface 1 on which a length of magnetic tape is taken up and an inner wall surface 3 formed with eight key ways 5 adapted to mesh with keys formed on a driving shaft, the inner wall surface defining an opening with which the ring can fit onto the driving shaft, said ring having a thickness substantially equal to the width of the magnetic tape. The inner wall surface has also four protrusions 9 so formed as to fit in correspondingly shaped key ways of an adjacent hub of the identical structure. These protrusions 9 serve as spacers when a plurality of such hubs are mounted on the driving shaft of a slitter, with the protrusions 9 kept in contact with those of the next hub. When the hubs in a stack are removed from the driving shaft and caused to turn relative to one another, their protrusions 9 fit in the corresponding key ways 5, reducing the overall thickness of the stack.
However, the conventional hub shown in FIG. 6, with a number of key ways formed along the inner periphery of the circular ring has problems of inappropriate roundness, backlash upon mounting on the driving shaft of a slitter, and difficulty of smooth mounting, with consequently low efficiency of operation. Moreover, the protrusions whose dimensions are dictated by those of the key ways are necessarily reduced in area, whittling down the stability. The present invention is aimed at settling all these problems of the prior art.